Cancer cells undergo dramatic changes in carbohydrate expression during the onset and progression of disease. Detection of these changes is essential for understanding their basic biology as well as for monitoring changes for diagnostic purposes. Carbohydrate expression is monitored almost exclusively with anti-carbohydrate antibodies and lectins. In addition, anti-carbohydrate antibodies and lectins can be used to target tumors. For these proteins to provide accurate information on the expression of carbohydrate tumor antigens or to reliably target tumors, they must bind specifically to a particular carbohydrate of interest. Unfortunately, analysis of specificity has been difficult with conventional tools and most antibodies and lectins have not been fully characterized. In spite of the lack of information, many of the antibodies and lectins are thought to be specific and conclusions regarding carbohydrate expression are made based on this perception. We have used a carbohydrate microarray to evaluate the specificity of commonly used anti-carbohydrate antibodies and lectins and found that many have specificity problems. We are using carbohydrate microarray technology to determine which antibodies are unreliable and to develop new antibodies/lectins with improved specificity. In addition, we are using the microarray to identify carbohydrate-binding proteins that interact with carbohydrate tumor antigens.